And installed it.
You can check that graphviz for python is trying to execute dot.exe tool (subprocess.Popen(cmd) in graphviz\files.py), so to solve the problem you can go to the graphviz directory and call pycallgraph:cd c:\Program Files (x86)\Graphviz2.38\binc:\Program Files (x86)\Graphviz2.38\bin>python c:\Python27\Scripts\pycallgraph graphviz -o main.png -- e:\main.py